The purpose of this study was to identify the exercise intensity equivalent to the aerobic/anaerobic metabolic transition in obese rats of both genders using the maximal lactate steady state (MLSS) protocol. Four groups of rats were tested on MLSS protocol (swimming exercise): male control n=10, female control n=10, male obese n=10 and female obese n=10, after suitable adaptation to exercise in liquid medium and obesity induction by monossodic glutamate (MSG) administration. The obese groups had significant increase in subcutaneous adipose tissue as well as mesenteric and retroperitoneal fat depots comparing to the control groups. The Lee index was higher in the obese animals in comparison to their respective controls. It was possible to identify the MLSS at 6.0% of body weight for both obese groups. Concerning the female control group, the MLSS was determined at the intensity of 5.0% of body weight, whereas for the male control at 4.5% of body weight. It was concluded that obesity induced by MSG interferes in lactate kinetics during exercise and alters the effort intensity corresponding to the metabolic transition in both genders.